In the last quarter century the use of brain imaging for the treatment and understanding of diseases and genetic flaws has grown dramatically following the introduction of Tomographic X-Ray (CT) in 1972 followed in 1982 by magnetic resonance in the gene (MRI). The reason for this growth and importance in brain imaging is that neurologists, psychotherapist, and neuro-scientists utilize and attached substantial importance to high resolution, three dimensional anatomical images of the brain. The development of functional brain imaging which seeks to map the distribution of brain activity has closely followed the development of structural imaging which maps some physical property of the brain such as tissue density. While SPECT is playing an important role in functional brain imaging, it has been limited in many applications by its low spatial resolution. The tiny structures of the brain where thinking takes place are much smaller than the resolution of the best SPECT scanners and therefore are not seen. Only in the situations where gross functional changes or small changes over a large population of subjects have occurred is SPECT useful.
U.S. Pat. No. 4,209,700 to Stoddart discloses a first generation nuclear transverse sectional brain function imager. Stoddart discloses an imaging apparatus having a transverse radio nuclide scanfield and a method for using highly focused collimators in an array surrounding the scanfield. This allows the scanner to concentrate its information gathering capability on a single cross-section of the head as opposed to the rotating gamma camera whose sensitivity is distributed over the entire volume of the head. In the situations where only part of the brain is of interest, this is a huge advantage, especially for dynamic studies where one needs to make rapid repetitive scans of the same area. The scanner is not limited to single sections. By moving the patient through the scanner, a stack of sections may be obtained which cover the entire volume of the head.
In general, the typical clinical resolution of the best SPECT rotating gamma-cameras is about 7 mm. This is inferior to both PET and fMRI which provide 5 mm and 3 mm resolution, respectively. The two avenues of improvement used to bring rotating gamma-cameras to their state-of-the-art are: 1) increasing the number of camera heads (now 3) and 2) modifying the original parallel hole collimator design to the higher performance mildly converging tapered hole designs' while increasing camera area in order to maintain a sufficiently large field-of-view (FOV). Further improvement is difficult since the cameras of 3-headed systems now totally encircle the patient with little room left for more or larger versions.
Collimators are simply blocks of lead with holes drilled through them (or cast with holes in them) to allow gamma rays to pass through which are traveling in a specific direction. The longer or narrower the holes, the more precise that direction becomes. This is good for geometrical resolution but bad for sensitivity and one needs both. Tapered holes are vastly superior than straight holes in that they provide both better geometrical resolution and sensitivity at the same time. While rotation gamma-cameras benefitted from mildly tapered holes, they cannot take advantage of highly tapered holes since the resulting FOV would not cover the entire head. The present scanning system overcomes this problem by sweeping the narrow FOV.